Lubrication fluid, such as oil, is generally pumped through a fluid pump in order to lubricate the moving parts of the pump. Mixing of the lubrication fluid with the fluid being pumped can undermine the lubricity of the lubrication fluid and/or contaminate the fluid being pumped with the lubrication fluid. For example, many fuel systems include a low pressure transfer pump that draws fuel from a fuel tank and a high pressure pump that increases the pressure of the fuel before injection. Lubrication fluid, generally oil, flows within the high pressure pump to lubricate the moving parts. Cam-driven, reciprocating pistons within piston bores of the high pressure pump increase the pressure of the fuel. The reciprocating motion of the piston and the pressure within the piston bore can cause some of the fuel to migrate between the piston and the piston bore. If the fuel is permitted to migrate outside of the piston bore and into a cam-housing region, the fuel will directly mix with oil, decreasing the lubrication quality of the lubrication oil, which can lead to potentially serious problems throughout the lubrication system.
In order to reduce the fuel migration between the reciprocating piston and the piston bore, it is known to position a seal, such as an o-ring, between the piston bore and the reciprocating piston. The seal blocks the migration of the fuel into the lubrication oil system. However, many fluid pumping reciprocating pistons can be subjected to relatively extreme pressure changes, thereby reducing the life and the sealing capability of the seals.
In order to relieve the pressure on a seal, being an o-ring, and further reduce fluid mixing, a fluid seal, described in U.S. Pat. No. 5,901,686, issued to Stockner et al. on May 11, 1999, is designed for a fuel injector that includes a reciprocating piston within a piston bore including a pressurization chamber in which fuel pressure is increased. The fluid seal includes an annular pressure accumulation volume defined by the piston and positioned between the pressurization chamber and the o-ring. A fuel injector body defines a pressure release passage positioned between the accumulation volume and the pressurization chamber and that fluidly connects the piston bore to a low pressure return line.
As fuel migrates between the piston bore and the piston when the piston advances to pressurize the fuel within the pressurization chamber, pressure on the o-ring is reduced by some of the fuel flowing from the bore to the pressure release passage while another portion of the fuel accumulates within the pressure accumulation volume. When the pressure accumulation volume of the advancing piston is aligned with the pressure release passage, the pressure on the o-ring dramatically drops being that the pressure accumulation volume drops to the same low pressure as the low pressure return line. The pressure with the accumulation volume will again build when the piston advances past the pressure release passage until the injection event ends.
Although the pressure on the o-ring is reduced by the combination of the pressure accumulation volume and the pressure release passage, the fuel migrating up the piston bore is still permitted to migrate and accumulate within the piston bore for the majority of the pressure stroke of the piston. Only for the brief time that the pressure accumulation volume is fluidly connected to the pressure release passage is the fuel within the pressure accumulation volume able to evacuate from piston bore.
The present disclosure is directed at overcoming one or more of the problems set forth above.